https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109339
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |hubicka at gcc dot gnu.org
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
OK, I suppose I was misled by trying to trace how the construction works. The
first half of my comment#2 still stands - we diagnose
ss ={v} {CLOBBER};
std::stop_token::_Stop_state_ref::_Stop_state_ref (&ss._M_state, &ss);
by (maybe broken) design, the &ss argument is a const reference which
we decide implies read. In this case we could even use modref to
see the parameter is unused - but the call happens through an alias
and in the -Og pipeline we do not run late modref.
The called body is
void std::stop_token::_Stop_state_ref::_Stop_state_ref (struct _Stop_state_ref
* const this, const struct stop_source & D.79270)
{
void * _5;
<bb 2> [local count: 1073741824]:
_5 = operator new (24);
MEM[(struct _Stop_state_t *)_5]._M_owners.D.16955._M_i = 0;
MEM[(struct _Stop_state_t *)_5]._M_value.D.16955._M_i = 0;
MEM[(struct _Stop_state_t *)_5]._M_head = 0B;
MEM[(struct _Stop_state_t *)_5]._M_requester._M_thread = 0;
MEM[(struct __atomic_base *)_5]._M_i = 1;
MEM[(struct __atomic_base *)_5 + 4B]._M_i = 4;
MEM[(struct id *)_5 + 16B]._M_thread = 0;
this_2(D)->_M_ptr = _5;
return;
}
but since this function can be interposed even modref doesn't help (when
scheduled and enabled) since it throws away this knowledge :/ Maybe
we need some optimistic mode for diagnostic code (or add
EAF_LIKELY_UNUSED).
But as said (late) modref isn't in the -Og pipeline and it's only enabled
with -O2+ anyway.
The other possible heuristic adjustment would be noticing &ss is also
passed as first non-const reference argument.
